It seems that if you look at the column on the right of the page, you can see upvotes and downvotes separately for recent posts. The same [n, m] format is displayed for recent comments, but it doesn't seem to actually sync with the score displaying on the comment. This feature only seems available on the sidebar: looking at the actual comment or post doesn't give you this information.
Thanks, whoever did this!
It appears to me that 30 day karma has switched back to votes received in the past 30 days from votes on material posted in the past 30 days. Why? The original switch was very soon after the introduction of the feature.
I noticed this because people who haven't posted in months have 30 day karma. I then tested it by voting on an old comment.
You're correct, John deliberately changed this as he thought it was a bug. I'll chat to some people to work out what the desired behaviour is.